The present invention relates to a tubular casing and to a process for its manufacture. More particularly, the invention relates to a tubular casing made from a web, for example, of regenerated cellulose, by folding the web along the longitudinal axis and gluing the over-lapping edge zones running along the longitudinal axis. See, e.g., U.S. Pat. No. 2,148,884, No. 2,226,442, No. 2,685,769, No. 2,685,770 and No. 2,757,495. The gluing operations hitherto described, however, comprise either the use of solvents with which the surface of the web is partly dissolved and is tackified, whereupon an "adhesive" is produced in situ on the surface of the web, or the use of webs which are coated with a thermoplastic resin or consist of a thermoplastic material which can be sealed when heat and pressure are applied. See, e.g., U.S. Pat. No. 2,773,773. Acrylates which can be tackified by application of heat or by means of a solvent are also mentioned as examples of suitable resins in U.S. Pat. No. 2,653,432. Furthermore, it has already been proposed to use an acid solution of a water-soluble, partially polymerized thermosetting resin as the adhesive agent, with polymerization of the resin being accelerated by the presence of an acid (pH 4.5-5.5) in the aqueous solution. In U.S. Pat. No. 2,607,696, examples of these resins which are mentioned are aminoplast resins, such as urea/formaldehyde or melamine/formaldehyde resin, ketone/formaldehyde resins and phenolic resins which are hardened at 180.degree. to 220.degree. C. and thereby glue the overlapping edge regions which have been pressed together. U.S. Pat. No. 2,686,725 proposes a process in which the thermosetting resin, for example, a melamine/formaldehyde resin, is applied in acid solution, for example, to the still moist fiber-free cellulose gel which has not yet been dried, and a heat-sealing layer of polyethylene resin in the form of a tape or as a powder is melted onto the subsequently hardened resin. In order to bond the overlapping edge regions of the cellulose hydrate web, the polyethylene is melted under the application of pressure and elevated temperature and the overlapping edges are heat-sealed to one another.
It is common to all these tubular casings that they can be manufactured only in a relatively troublesome manner, i.e., at high temperatures, with long residence times until the adhesive has set and with the aid of acids or organic solvents which can be removed from the tubular casing only with difficult and very expensive measures. Furthermore, they are not sufficiently permeable to gas and smoke in the gluing region. For these reasons, tubular casings have for many years been predominantly manufactured without a seam; however, because of the relatively slow web speed, this tubular spinning process is very costintensive and permits only a limited tube diameter. In addition, it is not entirely possible to achieve a uniform tube diameter and wall thickness; and finishing processes, for example, coating the inside of the tube, are very complicated and expensive to carry out. In addition, in the field of tubular casings which are provided with a lengthwise seam, there have been hardly any publications in recent years which give an indication as to how the problems mentioned above could be overcome.